Lecture 4- Comparative studies of primates Flashcards
What is evolution?
-The change (over time) of inherited traits found in populations of individuals • Evolution is a genetic change • Not design, or predetermined by the organism - e.g. primates did not decide to grow strong arms to swing through trees • Rather, natural selection favours individuals that have traits that give them an advantage, meaning they are more likely to survive and reproduce. • These adaptations are inherited by their offspring. -change of appearance through behaviour is not evolution! evolution is not design!
Can we see evolution?
-extremely rare to see but can infer evolution from observing diversity
How to avoid telling “just so” stories?
-the case with Abbott Handerson Thayer -father of modern camouflage -identified the importance of counter-shading -but then he went overboard and saw camouflage everywhere (like on a peacock’s tail which makes no sense)
What is counter-shading?
-on aquatic animals, light colour on their underside and darker hue on the top
What is disruptive colouration?
-e.g. in zebras, it serves a function -so predators are unable to tell how many zebras there are and where one begins and the other ends
How to reduce storytelling?
-arguments strengthened if more than one species exhibits the behaviour or characteristic for the same purpose (e.g. Animals with spots) -if have several species that exhibit a similar characteristic and live in environments where the trait makes sense
What did Pliny the Elder observe about the fecundity of animals?
-Larger animals are less fecund. Elephants, camels and horses produce one offspring at a time; the thistle- thrush, the smallest of birds, twelve
What is a life history?
• Event diary of an organism’s life • Encompass three major biological processes: 1. Growth (gestation length, newborn weight, age and weight at weaning) 2. Ageing (age at sexual maturity, lifespan) 3. Reproduction (number of offspring produced, frequency of offspring production) -eg. an elephant has one large offspring and a very long gestation period
What do you use comparative data for?
- To group together organisms - basis of classification and phylogeny 2. To test hypotheses about adaptation - the Comparative Method
What are the correlates of life history and body size?
- majority of the attributes are positively correlated, if you are big= long gestation
- litter size is negative= the bigger you are the smaller the smaller litter size you have
What is the relationship between sexual maturity and lifespan (primates)?
-the longer the lifespan the older the individuals are at reaching sexual maturity
What is the relationship of lifespan and body mass in primates if you control for body mass by calculating residuals?
- take a residual of the relationship, take distance of the first red, then take the second and plot the differences
- relationship between age at maturity and lifespan is not independent of body mass
Why is there a need to incorporate information about evolutionary relationships into comparative studies?
• Phylogeny can complicate comparative analyses • Closely related individuals or species share characteristics because of shared inheritance -Therefore they are not independent samples -we need to control for phylogeny
What is the example that shows we need to control for phylogeny?
-blue eyes and big toes, if you sample close relatives you are likely to get a correlation -when comparing individuals with shared inheritance, genetics - not independent samples! -important to account for the relatedness of individuals before doing comparative studies
What is a baculum?
-a bone in the penis of most primates
What is the story about the evolution of the primate baculum?
• Important in sexual competition between males?
- Prediction: polyandrous species have bigger bacula than monandrous species, if competitive should have a larger bone in the penis
- when you look at the graph on the left it shows that polyandrous species have a larger baculum
- but on the right graph it shows when you account for relatedness (since most monoandrous species come from one family) the relationship disappears
What is the story about the evolution of trichromatic vision in primates?
-it appears that once you have colour vision there is a tendency for having colourful ornaments, increase in sexual dimorphism and evolution of more complex mating systems
-so can ask has red colouration evolved more often in lineages with colour vision than would be expected by chance?
- to answer this utilise the concentrated changes test
- answer: Yes: Probability of this distribution of red pelage in primates with colour vision occurring by chance < 0.05
-then another question: Have polygamous mating systems evolved more often in lineages with colour vision than would be expected by chance?
-answer:Yes: Probability of polygamous mating systems being found only in primates with color vision occurring by chance < 0.01
What is the example of using independent contrasts?
lot of similarities between individuals are due to the shared genetics
- if there are differences between related= can use the differences as independent
- we need to look at the independent difference between the chimpanzee and human = calculated the difference between the averages
- changes in weight and lifespan
- independent evaluation of the traits -shows slight negative relationship= larger tend to live shorter
What is another example of using independent contrasts?
- Does mating behaviour have consequences for the immune system in primates?
- Predict: species where females have more mating partners will have stronger immune systems (higher white blood cell counts) to counter risk of sexually transmitted diseases
- if have lot of partners= more likely exposed to more parasites, so the ones alive should be more immune
- how good immune system and promiscuity correlate= quite well
